1. Field of the Invention
This invention relates to an anti-skid fluid pressure control apparatus.
2. Description of the Prior Art
FIG. 1 shows a conduit system of an anti-skid fluid pressure control apparatus of a Prior Art. In FIG. 1, two fluid pressure generating chambers are formed in a cylinder body 3 of a tandem master cylinder 1. A brake pedal 4 is connected through a booster 2 to the cylinder body 3. By depressing the brake pedal 4, fluid pressures are generated in the two fluid pressure generating chambers respectively. The fluid pressures are transmitted through conduits 5a, 5b, electro-magnetic inlet valves 17a, 17b to wheel cylinders of a left front wheel FL and a right rear wheel RR. The conduits 5a, 5b are divided into conduits 7a and 6a, and, 7b and 6b respectively. Electro-magnetic inlet valves 20a, 20b having the same constructions as the inlet valves 17a, 17b are connected in the conduits 6a and 6b. They are connected to wheel cylinders of a right front wheel FR and a left rear wheel RL. The fluid pressures are transmitted through the conduits 6a, 6b and inlet valves 20a, 20b to the wheel cylinders of the wheels FR and RL. Further, the wheel cylinders of the wheels FL, FR, RL, RR are connected through brake relieving conduits 8a and 8b to low-pressure hydraulic reservoirs 25a and 25b. The hydraulic reservoirs 25a and 25b have the well-known construction. A piston is slidably fitted into a casing and urged by a relatively weak spring in the hydraulic reservoir 25a, 25b. Fluid reserving chambers of the hydraulic reservoirs 25a and 25b are connected to suction side of a fluid pressure pump 10.
The fluid pressure pump 10 has the well-known construction. It consists of an electric motor 11, an eccentric mechanism 12 and check valves 15a, 15b, 13a and 13b. A pair of plungers are moved backwards and forwards in the opposite directions. With the movement of the pair of the plungers, the check valves 13a and 13b, 15a and 15b are alternately opened and closed. Thus, the pressurized fluid is supplied to the conduits 5a and 5b.
Wheel speed sensors are associated with the wheels FL, FR, RL and RR, although they are not shown. When the vehicle provided with the apparatus of FIG. 1, is running on the road, the rotational speeds of the wheels FL, FR, RL and RR are detected by the not-shown wheel speed sensors. The outputs of the wheel speed sensors are supplied to a control unit 30. The control unit 30 has the well-known circuit construction and it judges the skid conditions of the wheels FL, FR, RL and RR. By the judgement results, the above described change-over valves 17a, 17b, 20a, 20b, 23a, 23b, 24a and 24b are selectively energized or deenergized.
For facilitating the understanding, it is assumed that all of the four wheels FL, FR, RL and RR are in the same skid conditions. When the brake pedal 4 is depressed, the pressurized fluid from the master cylinder 1 is transmitted through the conduits 5a 5b, and the inlet valves 17a, 17b, 20a and 20b to the where cylinders of the wheels FL, FR, RL and RR. According to the surface condition of the road and the manner of depressing the brake pedal 4, the control unit 30 now judges that the brake should be maintained at constant. Thus, solenoid portions s of the inlet valves 17a, 17b, 20a and 20b are energized. Thus, these change-over valves are put into the cut condition. Accordingly, the pressurized fluid are held in the wheel cylinders of the wheels FL, FR, RL and RR. Thus, the braking force is maintained at constant. Next, the control unit 30 judges that the brake should be relieved. Thus, the solenoid portions s of the outlet valves 23a, 23b, 24a and 24b are energized, while the solenoid portions s of the inlet valves 17a, 17b, 20a, 20b remain energized. Accordingly, the pressurized fluid from the wheel cylinders of the wheels FL, FR, RL and RR are discharged through the conduits 8a and 8b into the hydraulic reservoirs 25a and 25b.
Next, the control unit 30 judges that the brake should be reapplied. In this Prior Art, the brake is stepwisely increased. Accordingly, the solenoid portions s of the outlet valves 23a, 23b, 24a and 24b are deenergized, while the solenoid portions s of the inlet valves 17a, 17b, 20a and 20b are intermittently energized and deenergized. Thus, the fluid pressure is stepwisely increased in the wheel cylinders of the wheels FL, FR, RL and RR.
Next, details of the inlet valves 17a, 17b, 20a and 20b of the Prior Art will be described with reference to FIG. 2. They have the same construction. Representatively, the inlet valve 17a will be described. In FIG. 2, a bobbin 32 is supported on a coil support member 30. An electro-magnetic coil 33 is wound on the bobbin 32 and it corresponds to the solenoid portions s of the inlet valves 17a, 17b, 20a and 20b in FIG. 1. A casing 36 and a guide member 35 are arranged along the central axis of the coil 33. They are combined with each other in a coil casing 31. An armature 34 and a rod 37 contacting with the armature 34 are slidably fitted into the casing 36 and the guide member 35, respectively. The armature 34 is driven downwards by energizing the coil 33. An O-ring 38 and a cup-seal 39 are fitted onto the guide member 35. Although not shown in FIG. 2, the other inlet valves 17b, 20a and 20b and outlet valves 23a, 23b, 24a and 24b and the fluid pressure pump 10 are liquid-tightly arranged commonly in a casing block K.
A steel valve ball 44 is fixed to a lower end of the rod 37. It faces a valve seat 40b formed at an upper end of a valve seat forming member 40, at a distance from each other by a valve lift L. A coil spring 45 is pressedly extended between the rod 37 and the valve-seat forming member 40. It urges the rod 37 upwards. Thus, the rod 37 is positioned at an upper position as shown in FIG. 2. A path 40a of the rod 37 communicates with the conduit 5a connected to the master cylinder 1. And a valve chamber 42 formed in the guide member 35, in which the valve ball 44 is arranged, communicates with the conduit 7a connected to the wheel cylinder of the wheel FL.
The inlet valve 17a of the Prior Art is constructed as in the above described manner. When an energizing signal is supplied to the electro-magnetic coil 33 as the solenoid portion s from the control unit 30, the armature 34 is magnetically attracted downwards. The rod 37 is pushed and moved downwards with the armature 34. The valve ball 44 fixed to the lower end of the rod 37 comes to seat on the valve sheet 40b. Thus, the master cylinder side is cut off from the wheel cylinder side. When the energizing signal is cut off, the rod 37 is moved upwards by the spring force of the coil spring 45. Thus, the valve ball 44 is separated from the valve sheet 40b and the brake fluid is returned into the master cylinder.
The inlet valves 17a, 17b, 20a and 20b are constructed as in the above described manner. Although the outlet valves 23a, 23b, 24a and 24b are usually put in the cut state, they are constructed as in the above described inlet valve. As clear from FIG. 2, the brake fluid is flowed into the wheel cylinder side through the valve lift L or the space between the valve ball 44 and the valve seat 40b. When the vehicle provided with the apparatus of FIG. 1 is large such as a truck, the amount of the brake fluid from the master cylinder into the wheel cylinder on braking is large and so a large amount of the brake fluid is returned from the wheel cylinder into the master cylinder on brake-relieving. Thus, in accordance with the amount of the brake fluid on braking and relieving, the magnitude of the valve ball 44 and so the magnitude of the valve seat such as an opening angle is determined. When the amount of the pressure fluid is large, the valve ball 44 is large and the valve lift is long. Accordingly the spring force of the spring 45 and the capacity of the electro-magnetic coil 33 for driving the armature 34 and the rod 37 should be large. As the result, the entire of the valve apparatus becomes very large.
Accordingly, when the anti-skid control fluid pressure control apparatus as shown in FIG. 1 and FIG. 2 is used for the automobile (passenger car), the capacity of the inlet valves 17a, 17b, 20a and 20b and the outlet valves 23a, 23b, 24a and 24b should be changed and larger for a larger vehicle such as a truck. If the inlet valves 17a,17b, 20a and 20b and the outlet valves 23a, 23b, 24a and 24b are standardized for the auto-mobile (passenger car), they should be manufactured by a special specification for the larger vehicle such as a truck. Accordingly, the cost of an anti-skid control apparatus for large vehicle such as a truck becomes high.